The purpose of this study is to determine whether intranasal administration of interleukin-12 (IL-12) will shift lung cytokine and antibody expression during immune responses and enhance the effectiveness of vaccination against respiratory pathogens. IL-12 may be especially beneficial for increasing the usefulness of viral vaccines since it stimulates production of interferon-gamma and secretion of antibody isotypes that are most efficient in mediating complement fixation and opsonization. For the experiments in this study, BALB/c and C57BL/6 mice will be inoculated intranasally with IL-12 and influenza or HIV-1 subunit proteins, and levels of induced cytokines and antibodies in the lungs and serum will be monitored at various times thereafter. The ability of IL-12 to cause shifts in cytokine RNA expression will be examined by RT-PCR and ribonuclease protection assays. The levels and specificities of induced antibodies will be quantitated using isotype-specific ELISAs. Intermediary cytokines potentially responsible for the observed protective capacity of IL-12 against lethal influenza infection will be identified using mice with targeted disruptions in cytokine genes and the role of endogenous IL-12 in regulating responsiveness will be examined using IL-12 knockout mice. Passive transfer of serum or bronchoalveolar lavage from intranasally immunized mice and immunodeficient mice lacking specific lymphoid cell subsets will be used to determine whether the protective effects of IL-12 are due to induced antibodies or activated cytotoxic T cells. Most parenterally administered vaccines have limited effectiveness at inducing optimal mucosal immunity and there are no suitable mucosal adjuvants available for clinical use at the present time. Thus, the application of IL-12 as a mucosal vaccine adjuvant may provide a novel approach for protection against respiratory diseases and could have immediate impact on human health.